Field of the Invention
The present invention relates to an image projection apparatus, such as a liquid crystal projector, which uses multiple light sources.
Description of the Related Art
The above image projection apparatus is capable of projecting a large and bright image by combining lights from multiple light sources to produce a high intensity light and by image-modulating the high intensity light with a light modulation element such as a liquid crystal panel or a digital micromirror device (DMD). In such an image projection apparatus, in particular in one using multiple light sources such as discharge lamps that require cooling, all of the light sources should be sufficiently cooled. The reason for this is that an insufficiency in the cooling of the light sources increases a rate of speed at which a brightness (light-emission amount) of each light source decreases, which significantly shortens a lifetime of each light source.
As a method of extending a lifetime of a light source included in an image projection apparatus, Japanese Patent Laid-Open No. 2000-338601 discloses a method of providing multiple light sources to the image projection apparatus and switching, at every start-up of the apparatus, one light source to be lit.
On the other hand, an excessive cooling of the discharge lamp makes a state of enveloped substances such as gas and metal fume fever included in the lamp unstable, which makes it impossible to achieve a stable light emission. For this reason, temperature control of the discharge lamp is important. Japanese Patent Laid-Open No. 2010-032944 discloses a method of controlling, in an image projection apparatus provided with multiple light sources, number of rotations of a cooling fan depending on lighting states of the light sources.
Furthermore, a change of an installation position (e.g., flat installation or upright installation on an installation surface, or ceiling mounting) of the image projection apparatus results in a variation in a temperature distribution around and in the light source. For this reason, it is necessary to perform the cooling and the temperature control of the multiple light sources depending on the installation position of the image projection apparatus. However, Japanese Patent Laid-Open Nos. 2000-338601 and 2010-032944 disclose nothing about the cooling and temperature control of the light sources depending on the installation position of the image projection apparatus. This means that the lifetime of any of the multiple light sources may be significantly shortened depending on the installation position of the image projection apparatus.